The purpose of the present plan of research is to examine the underlying mechanisms that allow for the normal development of depth perception in human infants. Because basic perceptual abilities constrain cognitive and language development, it is essential to describe the perceptual mechanisms that guide behavioral development. Depth perception is one of the most important perceptual capacities because it enables such common abilities as size and shape constancy and the perception of unitary objects despite stimulation captured separately by the two eyes. To examine the development of depth perception, a series of three experiments is proposed. Stereopsis refers to binocular depth perception and it will be assessed in 2- and 5-month-old infants using an automated corneal reflection eye monitoring system and dynamic random element stereograms. Tracking eye movements will be recorded as the infants view either a single moving stereoscopic form or a set of stereoscopic stripes. The goal of these detailed eye movement recordings is to provide a more rapid and sensitive assessment of stereopsis than is provided by current preferential looking techniques. Vergence eye movements used to binocularly fixate the stereograms will also be recorded to determine any developmental improvements in the accuracy of ocular alignment between the youngest and oldest infants. Gross vergence inaccuracies and/or highly variable binocular fixation in 2-month-old infants could partially explain the emergence of stereopsis during the fourth postnatal month. Data from these experiments will provide not only information about the course of binocular development in young human infants, but also the basis for a potentially useful technique for the rapid assessment of stereopsis in clinical settings. Thus, normative data on the development of stereopsis will define the limits of information that is potentially available for other aspects of behavioral development such as maternal recognition, object permanence and locomotor behavior.